The present invention generally relates to electrical connectors. More specifically, the present invention relates to connectors having circuit protection.
Electrical overstress transients (“EOS transients”) produce high electric fields and high peak currents that can render circuits, or the highly sensitive electrical components in the circuits, temporarily or permanently non-functional. EOS transients may arise, for example, from an electromagnetic pulse, an electrostatic discharge, e.g., from a device or a human body, lightning, a build up of static electricity or be induced by the operation of other electronic or electrical components. An EOS transient can rise to its maximum amplitude in subnanosecond to microsecond times and have repeating amplitude peaks.
The peak amplitude of the electrostatic discharge (ESD) transient wave may exceed 25,000 volts with currents of more than 100 amperes. There exist several standards which define the waveform of the EOS transient. These include IEC 1000-42, ANSI guidelines on ESD (ANSI C63.16), DO-160, and FAA-20-136. There also exist military standards, such as MIL STD 461/461 and MIL STD 883 part 3015.
Materials exist for the protection against EOS transients, which are designed to respond rapidly (i.e., ideally before the transient wave reaches its peak) to reduce the transmitted voltage to a much lower value and clamp the voltage at the lower value for the duration of the EOS transient. EOS materials are characterized by having high electrical impedance values at low or normal operating voltages and currents. In response to an EOS transient, the materials switch essentially instantaneously to a low electrical impedance state. When the EOS threat has been mitigated, these materials return to their high impedance state. These materials are capable of repeated switching between the high and low impedance states, allowing circuit protection against multiple EOS events.
EOS materials also recover essentially instantaneously to their original hill impedance state upon termination of the EOS transient. EOS materials can switch to the low impedance state thousands of times, withstanding thousands of ESD events, and recover to the high impedance state after providing protection from each of the individual ESD events.
Circuit components utilizing EOS materials can shunt a portion of the excessive voltage or current due to the EOS transient to ground, protecting the electrical circuit and its components. The major portion of the threat transient, however, is reflected back towards the source of the threat. The reflected wave is either attenuated by the source, radiated away, or re-directed back to the surge protection device which responds to each return pulse until the threat energy is reduced to safe levels.
EOS devices, such as devices employing a polymeric voltage variable material (“VVM”) have been typically provided in the form of discrete components, for example, surface-mountable to a printed circuit board (“PCB”). While these devices have enjoyed considerable commercial success, they do have certain limitations.
First, it is always desirable for cost, spacing/flexibility and reliability purposes, to reduce the number of components that are required to be mounted to the PCB. Adding an overvoltage protection device to a board layout needing protection consumes valuable board space and adds to the potential for defects and electrical mismatching.
Second, adding components to a PCB requires a redesign or an incorporation into a currently pending design, which requires that the application is not yet in production or that a new release will have to be made. The majority of existing equipment cannot therefore make use of voltage variable materials without a significant redesign.
Third, transient voltage spikes emanate from events that occur outside of the PCB and are transmitted to the PCB through cables and wires. For instance, networked computer and telephone systems are subject to a variety of transients caused by environmental and handling activities. In these situations, it would be desirable to eliminate transients or overcurrent conditions before they reach the PCB, that is at the connector or cable level. Most overvoltage protection devices today are surface-mountable for the reason that the PCB has provided the most convenient place to mount the devices.
Also, certain peripheral devices that operate in a system environment, such as a disk drive, may not be currently protected by overvoltage protection devices that are located on the PCB. It is therefore desirable to provide a way to protect these peripheral devices.